Concrete Curing: Plastic Shrinkage Cracking, Bleeding, Evaporation, and Temperature

1. Concrete Curing: Plastic Shrinkage Cracking, Bleeding, Evaporation, and Temperature Jennifer A. Distlehorst Cliff Hobson Dave Meggers John Wojakowski Kansas DOT

2. Plastic Shrinkage CrackingAnalysis of the term • Plastic - capable of continuous and permanent change in any direction without breaking apart • Cracking - breaking apart or splitting

3. Plastic Shrinkage Cracking

4. Plastic Shrinkage Cracking Factors • Evaporation Rate - Menzel, 1954; Lerch,1957 • Combination of 4 Factors - Concrete and Air Temperatures, Humidity and Wind Speed • Critical Value from Lerch, 1957 – 0.2 lb/sq ft/hr • Bleeding of the Concrete • Are Today’s Concretes Still the Same? Similar? • New Value for regular, let alone high performance concrete?

5. Bleed Test of Concrete ASTM C 232

6. 0.2 0.15 0.1 0.05 Bleeding of Concrete and Loss of Water at Various Evaporation Rates 0.6 Laboratory Concrete, Air Entrained 0.5 0.4 0.3 Cumulative water bled or evaporated, lb/ft2 0.2 0.1 bleed water 0 0:43 1:26 2:09 2:52 time in hours

7. I-635 Example - Hand Placement 0.6 0.5 Dump 10:35 Consolidation 10:40 Tining 10:45 Curing Compound 10:50 92-95 F, ADJACENT CURED CONCRETE 106 F 0.4 0.2 Cumulative water bled or evaporated, lb/ft2 0.3 0.2 0.1 Measured evaporation rate 0.07 lb/sq.ft/hr 0.1 bleed water 10:30 11:00 11:30 12:00 time of day

8. Curing Compound 3:40 Consolidation 2:10 Tining 3:00 Dump 2:05 I-70 Example -Slip Formed 0.6 0.5 0.2 0.4 Cumulative water bled or evaporated, lb/ft2 0.3 0.2 evaporation 0.12 lb/sq.ft/hr 0.1 0.1 bleed water 2:00 2:30 3:30 4:00 3:00 time of day

9. Curing Compound 2:18 Tining 2:10 Dump 1:17 Louisburg Example - Slip Formed 0.6 0.5 0.4 0.2 Cumulative water bled or evaporated, lb/ft2 0.3 0.13 lb/sq.ft/hr 0.2 0.1 0.1 bleed water 1:30 2:30 3:00 2:00 time of day

10. Burlap 10:45 Dump 8:50 I-635 Bridge Example 0.6 0.5 Consolidation 9:00 0.4 Grade 30, Field Concrete 0.2 Cumulative water bled or evaporated, lb/ft2 0.3 0.1 0.2 0.1 0.05 lb/sq.ft/hr bleed water 9:00 10:00 10:30 9:30 time of day

11. If the evaporation rate is greater than the bleeding rate why isn’t there a lot of plastic shrinkage cracking in our concrete? • Stiffer, cohesive concrete (used in slip form paving & bridge decks) has some tensile strength to resist the force imposed by the surface tension of water • Water reducers used in these mixtures reduce the surface tension of the water

12. KDOT Bridge Deck Curing Specification 90M/R-91-R13* • Measure the evaporation rate on the bridge deck regularly • Use monomolecular/precure immediately after the bridge deck finisher • Fog immediately behind the tining float • Produce a gloss to a semi-gloss sheen without water runoff

13. KDOT Bridge Deck Curing Specification 90M/R-91-R13* • Apply curing compound to the damp wearing surface • Cover with wet burlap for seven days • Use soaker hoses • Polyethylene sheeting is not allowed until the evening of the day following placement if the temperature is forecast to be above 50 F

26. Temperatures of a Slab Bridge 15 F PLASTIC PLACED Air N N N N N N = noon N

27. Evaporation retarder applied immediately E. Holt, Concrete International , Sept 2000 (0.1 psf = 0.02 in) E. Holt, Concrete International , Sept 2000

28. Water applied after 1 hour E. Holt, Concrete International , Sept 2000 (0.2 psf = 04 in)